I had been across it dozens of times on bike, on foot, and in 4×4, but never realized it was there. An aqueduct. The reason I had noticed it this time were the recent signs of machinery used to clear the ditch of debris and vegetation.
I followed it to the north where it joined up with a stream and a diversion. Then I followed it south where it became elevated as it crossed a gulch. The water sitting in it was still half-frozen.